An ion optical apparatus is mainly used as an ion transmission or guiding device in a mass spectrometer so as to introduce ions generated from an ion source into a mass analyzer. An ion optical apparatus in the form of an electrode array, e.g., those described in U.S. Pat. Nos. 6,107,628 and 8,581,181 as well as Chinese Patent CN201210203634, etc., has been widely used in the industry due to its flexibility in design and function.
Currently, a process for fabricating an electrode array mainly comprises the steps of directly fabricating a discrete pure metal electrode device, and then positioning and fixing it by a tooling fixture. The fabrication by pure metal electrodes has the following advantages: firstly, the machining precision can be very high and can easily meet the requirements of an ion optical device; and secondly, the device has no insulating portion itself, thus avoiding charge accumulation. However, such process is usually very complex, time-consuming and relatively expensive due to a larger number of electrode arrays; and a very large capacitance will be introduced by the electrode arrays, so a power supply with a very large power output will be required. To reduce the fabrication cost and capacitance, a better approach is to use a stacked printed circuit board (PCB), wherein edges of the PCB are coated with a metal coating as an electrode, while other pieces of PCB which are not covered with the metal coating serves as the insulting layers, and then multiple PCBs are stacked to form an electrode array. Although the PCB process is mature, tooling is required for positioning in the multiple-piece stacking process, which involves a relatively complex procedure. In addition to the edges of the PCB, the surface of the PCB can also be plated with an electrode to form an ion optical device, for example, the PCB process is used to fabricate the flight tube, the acceleration electrodes, the mirror electrodes, etc. of a time-of-flight mass spectrometer in U.S. Pat. No. 6,316,768, and the PCB process is also used to fabricate a planar linear ion trap in U.S. Pat. No. 7,498,569.
In addition, in recent years, with the rapid development of a micro/nanofabrication technology and a micro-electromechanical system (MEMS), many people have begun to apply them to the fabrication of ion optical devices, especially ion traps. Although the nanofabrication technology emphasizes a three-dimensional structure compared with a PCB technology in a conventional IC process, a planar metal coating on the surface of an insulating layer is mainly used as an electrode in the current ion optical devices (see, for example, U.S. Pat. Nos. 7,217,922, 7,402,799, 8,213,118 and 8,299,443).
Although there have been numerous examples of the mature PCB process and the rapidly-developing MEMS process applied to ion optical devices, a cell electrode of an electrode array itself has so far been only used as a voltage applying point or surface, so the cell electrode takes the shape of a simple geometric configuration such as a point, a line or a rectangle. Accordingly, numerous cell electrodes and a matching power supply system are needed to obtain a certain complex potential distribution, or the three-dimensional electrodes with very complex structures can only be used to form a desired corresponding spatial electric field distribution.